Fibre reinforced polymer components, otherwise known as polymer composite components, consist of reinforcing fibres held together with a polymer resin, often known as the matrix. This matrix can be a thermosetting polymer such as an epoxy resin, in which case the composite component can be called a thermosetting composite component, or a thermoplastic polymer, also known as a thermoplastic, such as polyamide or polyetheretherketone, in which case the component can be called a thermoplastic composite component. It should be noted that a thermosetting composite component may contain small amounts of thermoplastic polymer, for instance as a surfacing film, a resin additive, or a binder agent. A thermoplastic composite component may in the same way contain small amounts of thermosetting polymer, for instance in a core or insert.
The majority of structural polymer composites have a thermosetting matrix. Therefore techniques for joining other components to these structural polymer composite components are based on the standard methods available for joining of thermosetting composites, mechanical fastening and adhesive bonding. These joining processes can be slow processes, and therefore add considerably to the expense of assembly, even for the attachment of small components.
Small functional components, also known as attachments or fittings, and including stand-offs, studs, bushings, and brackets, and similar items, are used to attach various things to structural thermosetting composite laminates and structures. Such functional components are traditionally metallic, but may also be made with thermoplastic, reinforced thermoplastic, fibre-reinforced composites of different sorts, and other materials, or combinations thereof. A high strength attachment can be obtained between such a functional component and a composite material if the functional component is embedded in the composite material prior to cure. However this is not always possible and frequently inconvenient. Attachment therefore is accomplished through the use of mechanical fasteners or adhesives to join the functional component. These methods are those that would also normally be used for joining functional components to structures made of metals and other materials. Mechanical fasteners provide high-strength attachment to composite laminates; however the attachment requires the drilling of holes in the composite laminate, resulting in a potential reduction in mechanical properties in the composite laminate. In many scenarios, it is far preferable to attach the functional component by adhesive bonding. However where adhesives are used, the functional components may be capable of far greater load carrying capacity than the adhesive bond. An additional barrier to strong adhesive bonding can occur when the composite component has been painted. In this circumstance, the strength of an adhesive bond is often governed by the low level of adhesion between the paint and component. Frequently this requires removal of paint in the vicinity of joining the functional component, in order to obtain reliable attachment.
Cheap and readily mass-produced functional components can be made of thermoplastic or reinforced thermoplastic, either wholly or in part. These have not been readily adopted, however, in part due to the difficulty in obtaining good adhesive bonds with such components. In order to make a high strength adhesive bond between a thermoplastic functional component and a thermosetting composite, the surfaces of both the thermosetting composite and thermoplastic functional component normally require surface treatment. In the case of the thermosetting composite this can be abrasion of the surface and cleaning with an appropriate solvent. In the case of the thermoplastic this can be one of a range of treatments such as corona discharge or gas-plasma treatment.
It is therefore desirable for the present invention to alleviate, at least in part, one or more of the above problems by providing a method for attaching a functional component, made partially or entirely of thermoplastic, to a thermosetting composite laminate or component. Advantageously, the process may be used to attach a functional component to the thermosetting composite component with very high attachment strength. More advantageously, the process is very rapid, and can allow significant cost reduction in the attachment of functional components to thermosetting composite surfaces. The process can be applied to both painted and unpainted composite components.